Efforts are currently being made to recycle used disposable diapers and other sanitary articles. For example, Patent Document 1 discloses a method for treating used disposable diapers comprising efficiently separating a used disposable diaper and washing with water while sequentially transferring the used diaper from a first-stage washing tub to a second-stage washing tub using a continuous washing machine having a plurality of washing tubs arranged in series to enable constituent materials thereof to be reused. According to the method described in Patent Document 1, in addition to using hypochlorous acid for primary disinfection of the used diaper (Paragraph [0044]), superabsorbent polymer present in the disposable diaper is dehydrated using lime (Paragraph [0047]), and the chlorine component of the hypochlorous acid is removed from the used diaper in a rinsing step (Paragraph [0046]).